Configurations of anions of β-ketoaldehydes in solutions studied by i.r. spectroscopy

The i.r. spectra of the Li, Na and K salts of β-ketoaldehydes, RCOCH₂CHO (R = Me, Et, i-Pr and t-Bu) in DMSO, methanol and water were investigated. Assignments of bands to stretching modes of particular configurations of the enolate system were given. Influence of the cation radius on the Z,Z ⇌ E,E/Z,E equilibrium and of the substituent R on the E,E ⇌ Z,E equilibrium was observed. Shifts of the enolate bands in protic solvents were observed and hydrogen-bond formation accounted for this phenomenon.     

Assessing the activity concentration of β-emitters by means of the end-window g.m. tube

The activity concentrations of β-emitters including ³⁵S (0.15 MeV) and presumably also ¹⁴C (0.14 MeV) may be determined with satisfactory accuracy using an end-window G.M. counter. For single preparations (if weighed), the described procedure warrants that the standard error will not exceed 0.8%, if the amount of substrate is kept below 0.2 mg/cm², and if carrier-free solutions are avoided. With a minimum of 4 preparations per sample solution, the error of the mean should not exceed 0.4%,     

Radiation-Induced,Solid-State Polymerization of Derivatives of Methacrylic Acid. XI. Aspects of the Polymerization of Methacrylic Acid by γ-Irradiation

Aspects of the radiation-induced polymerization of methacrylic acid in the crystalline state have been investigated and utilized to evaluate the mechanism of polymerization. In particular, results for post-irradiation polymerization at 0°C after radiation doses of 0.1 to 2.0 Mrad support the concepts of Lando and Semen that chain initiation essentially all commences at the same time, that chain propagation continues without termination, and that termination of nonpropagating radicals proceeds simultaneously.     

Ring Cleavage of N-Alkylisothiazolilm Salts by Complex Metal Hydrides. Synthesis of β-Enaminothioketones

N-Alkylisothiazolium salts undergo ring cleavage when treated with complex metal hydrides to give β-enami-nothioketones in high yields.

The isothiazole nucleus is remarkably stable to chemical attack by reducing agents.¹ In fact, little work has been published on reactions involving reductive cleavage of the isothiazole ring. Thus, other azole systems as isoxazole are readily cleaved by catalytic hydrogenolysis whereas the isothiazole nucleus, in the same conditions, remains unchanged.² However there are instances in which ring cleavage occurs. For example, cleavage of isothiazole during lithiation at the 5-position gives a small proportion of a β-mercaptoenone resulting from the cleavage of the N-S bond.^3,4 Isothiazoles are reductively desulfu-rized by Raney nickel and this method has been used by Woodward in a remarkable synthesis of colchicine.⁵     

Study on degrees of mesomorphic zone of polymer. Ⅲ.Determination of the degree of crystallinity of Eucommia Ulmoides gum by VTFTIR and VTWAXD

Eucommia Ulmoides (EU) gum will crystallize easily at room temperature due to the regular trans-1,4-polyisoprene (TPI) molecular structure. Around the skeleton stretching vibration band of TPI, its FTIR spectrum showed 5 weak crystalline peaks decrease as temperature increase, and there are also two amorphous peaks (845 cm⁻¹ and 668 cm⁻¹) increase as temperature increase. According to this phenomenon, Variable Temperature Fourier Transform Infrared Spectrum (VTFTIR) and Variable Temperature Wide Angle X-ray Diffraction (VTWAXD) have been taken to analyze the degree of crystallinity of EU gum. In addition to the ratio of crystalline zone, the result determined by VTFTIR also involve the mesomorphic zone, which make it higher than the result determined by VTWAXD. Through the comparative analysis of VTFTIR and VTWAXD, it has been proved that the ratio of crystalline zone, mesomorphic zone, amorphous zone in EU gum were respectively 39.8%, 27.6%, 32.6% at room temperature. Based on the Density Measurement and the three-phase model theory, the density gradient function of the mesomorphic zone of EU gum was firstly proposed. Below 60 °C, the density of the mesomorphic does not change with the temperature, approximately 0.931g/cm⁻³. Above 60 °C, the density of the mesomorphic decreases with the temperature increasing, and finally drops to 0.905g/cm⁻³ at 80 °C, which is equal to the density of the complete amorphous zone.     

Effect of Catalase on Biocatalytic Synthesis of Pyruvate by Enzymes from Pseudomonas sp.

Pyruvate was produced from DL-lactate by a kind of green-chemical biocatalyst --cell-free extract from bacterial strain Pseudomonas sp. SM-6. Catalase in cell-free extract, whichcould stabilize the pyruvate formed by lactate oxidase, played an important role in pyruvatepreparation. The effect of catalase in conversion process was evaluated.     

The Structure of Cellulose by Conformational Analysis. 1. Cellobiose and Methyl-β-cellobioside

Conformational analysis studies on the tertiary structure of cellobiose and methyl-β-cellobioside were carried out by using calculations of van der Waals, H-bond, electrostatic, and torsional energy interactions between the atoms and groups of the molecules. Energy maps as functions of the rotational anglesΨo and Φ° of the glucosidic bond were obtained in increments of 20° and refined in increments of 1°. Two “primary” and one “secondary” conformations of minimum energy were obtained for both cellobiose and methyl-β-cellobioside, some of which are equivalent to results obtained by x-ray diffraction. The H-bond forces are shown to be, together with the van der Waals forces, the predominant factors in the fixation of the conformations of minimum energy. The position and energy contributions of the H-bonds patterns for the favored conformations are identified.     

Synthesis of γ-lactones by desymmetrization. A synthesis of (−)-muricatacin

A short synthesis of the natural potent cytotoxic agent (−)-muricatacin 1 and related unsaturated lactones from a versatile common intermediate, dienedioate 2, derived from d-mannitol or tartaric acid, is described. The strategy depends upon the desymmetrization of 7 by dihydroxylation and elaboration of the hydroxy alkyl sidechain. A route to unsaturated lactones is also described using a cis selective Wittig reaction. Since the enantiomers of 2 are available from the corresponding tartaric acids, this method provides access to both enantiomers of the described compounds and a wide range of derivatives.     

Hydrocarbon dispersion of nanospherical silica by a sol–gel process. 1. Tetraethoxysilane homopolymerization

This study focused on the preparation of a hydrocarbon dispersion of nanospherical silica using tetraethoxysilane homopolymerization by a sol–gel process catalyzed by NH₄OH in ethanol. The silica surface was rendered hydrophobic by the introduction of trimethylchlorosilane or trimethylethoxysilane as a terminator. Organophilic particles with diameters in the range 10–130 nm were obtained under controlled conditions. Nevertheless, the organophilic fraction dispersed in hexane was not greater than 62%. The homopolymerization reaction time was directly related to the particle size and, in some cases, its insolubility. High terminator concentration and low termination temperature favored the increase in the number of organophilic particles. The chlorine-containing terminator was more efficient in promoting the production of hydrocarbon hydrophobic nanospheres. Received: 21 February 2000/Accepted: 21 June 2000     

Characterisation of the metabolites of an antibacterial endophyte Botryodiplodia theobromae Pat. of Dracaena draco L. by LC–MS/MS

Botryodiplodia theobromae Pat. belongs to the endophytic fungi that live within the tissues of medicinal plants and produce bioactive natural products. The endophyte was isolated from the leaves of Dracaena draco L. The LC–MS-based metabolite fingerprinting of the ethyl acetate extract of B. theobromae with antibacterial activity led to the identification of 13 metabolites pertaining to various classes: dipeptides (maculosin and L,L-cyclo(leucylprolyl), alkaloid (norharman), coumarin and isocoumarins (bergapten, meranzin and monocerin), sesquiterpene (dihydrocumambrin A), aldehyde (formyl indanone), fatty alcohol (halaminol A) and fatty acid amide (palmitoleamide, palmitamide, capsi-amide and oleamide). This study reports for the first time, the LC–MS and LC–MS/MS identification of 13 known bioactive metabolites from the antibacterial ethyl acetate extract of B.theobromae isolated from the leaves of D. draco L.     

Organic reactions catalysed by modified enzymes part I. Alteration of the substrate specificity of α-chymotrypsin by the modification process

The substrate specificity of some modified α-chymotrypsin derivatives in the synthesis of peptides, using natural and synthetic acyl donors and several nucleophiles, is studied. A systematic study of the alteration of active sites by the modification method is carried out. The method used in the present paper consists of covalent bonding of external lysines of the enzyme with a hydrophobic polymer. Enzymes with several degrees of modification have been obtained. These derivatives present different hydrophobic characteristics, depending on the degree of modification. All the modified enzymes are active in hydrophobic solvents such as benzene, toluene or 1,1,1-trichloroethane but need a small amount of water to be activated (< 1.0%). High yields are obtained in the synthesis of peptidic bonds (100% > × > 60%). The modified enzyme has the same stereospecificity as the native enzyme, because only esters with L-configuration in the α-carbon are accepted as acyl donors. Nevertheless a greater number of acyl donors are accepted by the modified enzyme than by the native α-chymotrypsin, in the synthesis of peptides. On the other hand, the nucleophile subsite is more lipophilic in the modified enzyme than in the native α-chymotrypsin.     

On the study by D.S.C. of the unexpected ice melting at 0°C of emulsified aqueous saline solutions

Firstly, the behavior of droplets (Φ ≈ 1μm) of aqueous saline solutions dispersed within an emulsifying medium and subjected to steady cooling and heating is described. Droplets undergo freezing around a temperature T¹(x) and partial ice melting and total salt melting at the eutectic temperature T_E. This melting is followed by progressive melting of the remaining ice which ceases when the equilibrium temperature (T_e(x)) ice ⇆ solution is reached. Between T_e and T¹ the droplets are undercooled. Secondly, the results obtained when water crystallization occurs versus time at a fixed temperature _C, such as T¹(x) < > _C < T_e(x) are reported. During heating following crystallization at Θ_C, an unusual ice melting at 0° and/or ice melting ending at T & >; T_e(x) is noticed on the thermogram obtained by differential scanning calorimetry of the emulsion. This shows that pure ice or at all events less concentrated solutions must be present within the emulsion. A possible mechanism of crystallization at Θ_C is proposed.     

Polymerization of lactams. 99 Preparation of polyesteramides by the anionic copolymerization of ε-caprolactam and ε-caprolactone

Polyesteramides derived from the cyclic monomers ε-caprolactam and ε-caprolactone have been synthesized by the anionic polymerization and characterized. ε-Caprolactam magnesium bromide was employed as unique initiator giving high yield of copolymer across the whole range of monomer concentrations at 150 °C. Owing to a variation of the content of ester and amide component in polyesteramide backbone a large variety of materials having diverse physico-chemical and mechanical properties have been prepared. Materials prepared were examined for mechanical characteristic. Thermal properties were characterized using DSC, temperature modulated DSC, Hi-Res^TM TGA and DMA. Viscosity measurements were employed for molecular characterization.     

The characterization of and the evolution of molecular hydrogen by the μ-hydrido-bridged cyclodecyl cation. Relevance to the question of hydrocarbon protonation by superacids

The observable cyclodecyl cation is established as having a 1,5-μ-hydrido-bridged structure and most probably exists as a mixture of conformational isomers. This solution carbocation is unique in organic chemistry in that it evolves molecular H₂ at temperatures below -100°C to give the 9-decalyl cation. The mechanism of this reaction is postulated to involve a pentacoordinated carbocation intermediate or transition state with a structure identical to what one would get by protonating the bridgehead C-H bond of decalin. Since conversion of decalin to the decalyl cation in superacids is not accompanied by significant H₂ production, the mechanism of these two reactions must be different, and in the latter case could not involve a protonated pentacoordinate carbocation intermediate, as has been postulated.     

Comments on the Note on “Thermodynamic temperature differences from the ITS-90 for the correction of thermodynamic property data” by F. Pavese,P. Ciarlini,and P.P.M. Steur by J. Fischer,Chairman of WG4 of CCT

These are comments to a note from J. Fischer in publication.